Glycosylation: mechanisms, biological functions and clinical implications

Protein post-translational modification (PTM) is a covalent process that occurs in proteins during or after translation through the addition or removal of one or more functional groups, and has a profound effect on protein function. Glycosylation is one of the most common PTMs, in which polysaccharides are transferred to specific amino acid residues in proteins by glycosyltransferases. A growing body of evidence suggests that glycosylation is essential for the unfolding of various functional activities in organisms, such as playing a key role in the regulation of protein function, cell adhesion and immune escape. Aberrant glycosylation is also closely associated with the development of various diseases. Abnormal glycosylation patterns are closely linked to the emergence of various health conditions, including cancer, inflammation, autoimmune disorders, and several other diseases. However, the underlying composition and structure of the glycosylated residues have not been determined. It is imperative to fully understand the internal structure and differential expression of glycosylation, and to incorporate advanced detection technologies to keep the knowledge advancing. Investigations on the clinical applications of glycosylation focused on sensitive and promising biomarkers, development of more effective small molecule targeted drugs and emerging vaccines. These studies provide a new area for novel therapeutic strategies based on glycosylation.

Effects of detoxification process on toxicity and foreign protein of tetanus toxoid and diphtheria toxoid

Formaldehyde detoxification is a process for converting tetanus toxin (TT) and diphtheria toxin (DT) into tetanus toxoid (TTd) and diphtheria toxoid (DTd), respectively. The mechanism of this detoxification process has been investigated by several previous studies based on lab-scale toxoids. To obtain greater insights of the effects induced by formaldehyde, industrial TTd and DTd batches obtained from different detoxification processes were studied in this work. Using liquid chromatography-mass spectrometry (LC-MS), 15 and 20 repeatable formaldehyde-induced modification sites of TTd and DTd were identified, respectively. Toxoid which had a higher formaldehyde-induced modification rate observed by LC-MS, also had larger bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Aggregates which were observed on size exclusion chromatogram (SEC) were confirmed by SDS-PAGE and LC-MS. Formaldehyde detoxification also led to a decrease of isoelectric point (pI) values and an increase of retention on weak anion exchange (WAX) column. Specific toxicity tests were conducted to evaluate toxicity of the TTd and DTd samples obtained with different detoxification conditions. Results from the specific toxicity tests showed that all toxoids used in this study were qualified, including toxoids obtained from mild and drastic detoxification conditions. However, obtained from mild detoxification conditions had less aggregates and may lead to a higher degree of glycosylation in conjugate vaccines than the ones obtained from drastic detoxification conditions. Thus, we suggest that mild detoxification conditions should be used to obtain TTd and DTd. Furthermore, as well as studying the formaldehyde-induced modifications and toxicity in TTd and DTd, the effects of the detoxification process on foreign proteins were also investigated. An increase in foreign proteins were observed in the aggregate than in the monomer of the toxoids. Additionally, some foreign proteins in the monomer of the toxins transferred to the aggregate of toxoids due to the formation of cross-linking. To eliminate the risk of cross-linking foreign proteins to toxoids in vaccination programs, a purification process is necessary before the detoxification process and/or the use of toxoids in vaccines.

Simultaneous quantification of spike and nucleocapsid protein in inactivated COVID-19 vaccine bulk by liquid chromatography-tandem mass spectrometry

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) vaccines are the most promising approach to control the COVID-19 pandemic. There are eminent needs to develop robust analytical methods to ensure quality control, as well as to evaluate the long-term efficacy and safety of vaccine. Although in vivo animal tests, such as serum-based ELISA, have been commonly used for quality control of vaccines, these methods have poor precision, are labor intensive, and require the availability of expensive, specific antibodies. Thus, there is growing interest to develop robust bioanalytical assays as alternatives for qualitative and quantitative evaluation of complex vaccine antigens. In this study, a liquid chromatography tandem mass spectrometry method was developed using optimized unique peptides for simultaneous determination of spike (S) and nucleocapsid (N) protein. Method sensitivity, linearity, repeatability, selectivity, and recovery were evaluated. The amount of S and N proteins in 9 batches of inactivated COVID-19 vaccines were quantified, and their compositions relative to total protein content were consistent. We believe this method can be applied for quality evaluation of other S and/or N protein based COVID-19 vaccine, and could be extended to other viral vector, and protein subunit-based vaccines.

Molecularly imprinted solid-phase extraction of Chikusetsu saponin IVa from Panacis majoris Rhizoma

As the main active component of Panacis majoris Rhizoma, Chikusetsu saponin IVa has the activity of anti-oxidation, anti-inflammatory pain, and so on. Obtaining high purity Chikusetsu saponin IVa by simple purification steps is a prerequisite for its deep development. In this paper, the separation and purification of Chikusetsu saponin IVa were studied by molecular imprinting technique. By ultraviolet and visible spectrophotometry and computer molecular simulation, it was concluded that water-soluble 3-(2-carboxyethyl)-1-vinylimidazolium bromide ionic liquid was the best functional monomer compared with acrylic acid and acrylamide. The molecularly imprinted polymers were prepared by precipitation polymerization at 60℃ with Chikusetsu saponin IVa as template molecule, 3-(2-carboxyethyl)-1-vinylimidazolium bromide as functional monomer, ethylene glycol dimethacrylate as cross-linker, 2, 2'-azobisisobutyronitrile as initiator, and ethanol as porogen. The properties of molecularly imprinted polymers were studied by scanning electron microscopy, Fourier transform infrared spectroscopy, thermo-gravimetric analysis, nitrogen adsorption/desorption isotherm, and X-ray photoelectron spectroscopy. The maximum adsorption capacity was 171.33 mg/g, and the imprinting factor was 2.6. Finally, the polymers can be successfully used in the purification of Chikusetsu saponin IVa from Panacis majoris Rhizoma through a simple procedure, the content was significantly increased. The recoveries of the spiked samples for the CS-IVa ranged from 94.05 to 99.95% with relative standard deviation values lower than 2.67%. The results showed that the polymers demonstrated good adsorption capacity for Chikusetsu saponin IVa. Meanwhile, the polymers showed great stability and reusability during the application.

Hydrophilic carrageenan functionalized magnetic carbon-based framework linked by silane coupling agent for the enrichment of N-glycopeptides from human saliva

In this work, a magnetic graphene material coated with mesoporous silica was selected as the substrate, 3-glycidoxypropyltrimethoxysilane and polyethyleneimine were sequentially bonded through chemical reactions, and then carrageenan was successfully introduced by electrostatic interaction; finally, hydrophilic nanocomposite material was prepared. Due to the large number of hydrophilic groups, and polyethyleneimine was connected by means of chemical bonds, this material exhibits good hydrophilicity and stability for glycopeptide enrichment. In the actual enrichment process, nanomaterial exhibits high selectivity (1:500), high sensitivity (2 fmol), and good repeatability (five cycles). In addition, the synthesized material also shows a good enrichment effect in the face of actual complex biological samples, which captured 40 N-glycopeptides from human saliva, indicating the application potential for enrichment of N-glycopeptides.

Simultaneous determination of capsid proteins in nine-valent human papilloma virus vaccines by liquid chromatography tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry method was developed to determine nine types of capsid proteins simultaneously in nine-valent human papillomavirus vaccines. Signature peptides were optimized in terms of specificity, repeatability, determination accuracy and sensitivity. As a result, three signature peptides per capsid protein were obtained. The linear calibration curves were achieved in the range of 11.6-373.6 nmol/L (R²  > 0.998). Compared to our previous liquid chromatography-tandem mass spectrometry method, the current method was more sensitive (3.18-fold) and it can be used for quality evaluation of nine-valent human papillomavirus vaccines, unlike the previous method, which could only be used for bivalent human papillomavirus vaccines. Then, they were utilized to determine nine types of capsid proteins in nine-valent human papillomavirus vaccines from four different manufactures. Intraday and interday precision values for the determination of capsid proteins in nine-valent human papillomavirus vaccines were less than 6.8 and 9.1%, respectively. Recovery rates of all capsid proteins investigated were in the range of 80-120%. In addition, the current assay was used for determination of free capsid protein in nine-valent human papilloma virus vaccines, and the results were used to evaluate the adsorption rate of the adjuvant.